The huge sum represents a serious ratcheting up of Caring’s contributions to the Tories. It sees him elevated to a position normally filled by one of several multimillionaire hedge fund managers, whose sizeable donations to the party qualify them for membership of the elite “Leader’s Club” that grants them private dinners with David Cameron.

Caring’s donation of £296,000 eclipsed that of the entrepreneur David Brownlow, who gave £260,000, and of Ian Taylor, chief executive of oil trading giant Vitol, who handed over £208,500. Christopher Rokos, a hedge fund manager who keeps a very low profile and, like Cameron went to Eton and Oxford, donated £170,000.

It is the generosity of Caring, who owns The Ivy, Le Caprice and J Sheekey restaurants, which is the most intriguing. According to official donation records, the flamboyant tycoon with the equally flamboyant hair has not given the party any money for three years. In 2012 he donated just over £50,000 and in 2010 gave almost £170,000.

As back then, this year’s donations were made by providing auction prizes – including the use of his nightclub, Annabel’s – for the Tories’ Black and White ball, which raises millions for the party’s war chest. Some in Labour, reliant on donations from the unions, and which brought in only £1.6m between July and September this year, not even half the near £3.4m that flowed to the Tories, may view Caring’s support for the Tories as a squandered opportunity. In 2006 Caring lent Labour £2m in a major coup for Tony Blair’s party.

His shifting political allegiance comes as he expands his empire. The entrepreneur, who once owned the Belgo and Strada chains as well as Wentworth golf course, is rolling out the Ivy brand and that of Soho House, in which he owns a majority stake. He also reportedly has plans to develop Annabel’s – the most famous of his several London clubs and the only nightclub ever visited by the Queen.

Caring, who made his fortune in the clothing business before diversifying into leisure interests, is a colourful individual. He came to prominence in 2005 when he organised a “Napoleonic Ball” for the NSPCC in the Catherine Palace in St Petersburg featuring a performance by Elton John. The man who made his first fortune in the rag trade apparently spent £8m flying in 450 guests, including Bob Geldof and former US president Bill Clinton, by private jet for an event that raised £11m for charity. He lives in Hampstead, north London, in a house that reportedly boasts a ballroom, cinema, dining room that seats 30, and a two-acre garden with a lake. But his high profile has made him the subject of scrutiny and controversy. As a non-dom he legitimately pays UK tax only on offshore income and capital gains if brought into the UK.

But this may change. Chancellor George Osborne has pledged to abolish non-dom status for those who have lived in t he UK for more than 15 of the last 20 years.

Reuters reported that Caring legally bought UK property through companies in tax havens, which then made profits of more than £60m when the assets were resold. A spokesman told the news agency: “Any offshore income that has been made has been declared to the authorities ... all of his business deals are totally within the law.”

Earlier this year the Guardian reported how leaked documents revealed that Caring had collected £2.25m in cash from HSBC’s Swiss bank in Geneva. Since he made the unusual, untraceable transaction, the bank has introduced new controls on withdrawals over £6,600. Caring’s lawyers denied any impropriety when the story emerged.

The tycoon declined to talk to the Observer. Media reports have suggested that Tory party treasurer and hedge fund CEO Stanley Fink was the successful bidder for the night at Annabel’s, which allowed him and 140 guests to enjoy “an exquisite menu and extensive wine list”.